1. Field of the Invention
An apparatus consistent with the present invention relates to a servo writer for writing servo signals on tape-shaped recording media such as a magnetic tape, which checks whether or not the servo signals are written successfully, and corrects an abnormality if detected, such as a writing error. More specifically, an apparatus consistent with the present invention relates to a servo writer which corrects an abnormality without eliminating it from the medium, thereby preventing the waste of media.
2. Description of the Related Art
Conventionally, tape-shaped recording media such as magnetic tapes have been used as external recording media for computers, etc. Referring to FIG. 6, in order to increase its recording density, a large number of data bands DB each containing data are formed on a magnetic tape MT along the width (vertical direction in this figure). For example, four data bands DB1, DB2, DB3 and DB4 are formed as a set of data bands DB in FIG. 6. Each of the individual data bands DB1 to DB4 is further divided into multiple fine bands (not shown). Recently, each data band is being narrowed to increase the total number of the data bands, so that the recording density is further increased.
However, the magnetic tape MT continues to move slightly in its lateral direction while being transported, for various reasons. Inevitably, as the data band is narrowed, it is more difficult for a recording/reproducing head of a recording/reproducing system (not shown) to completely trace the data band. To overcome this disadvantage, servo signals are written on a magnetic tape prior to using. Then, the recording/reproducing system dynamically controls the position of the recording/reproducing head relative to the magnetic tape by using the servo signals during the record/reproduction stage. Specifically, the system uses its servo signal reading head to read from the magnetic tape, then senses the amount of the lateral displacement of the recording/reproducing head relative to the magnetic tape, and finally makes fine-movement of it in accordance with the sensed amount. As a result, the displacement is compensated. Note that, in the recording/reproducing system of this type, the servo signal reading head and the recording/reproducing head are integrated.
The servo signals are written on the servo bands SB1 to SB5 (see FIG. 6) of the magnetic tape MT in the transport direction (i.e. the direction of an arrow A) by using a dedicated servo writer.
A conventional servo writer is constituted as follows:    (a) a supply reel which feeds a magnetic tape;    (b) a write head which writes a servo signal on the magnetic tape;    (c) a verifying head positioned downstream of the write head, which inspects the servo signal; and    (d) a take-up reel that winds the magnetic tape.
Since the servo signal written by this servo writer is used as a reference for controlling the position of the recording/reproducing head, the servo signal must be written correctly without any absent and superfluous parts.
Therefore, the servo writer checks whether or not the servo signals are written successfully on the magnetic tape, by using its verifying head, after writing the servo signals with its write head. If an abnormality is detected, then the servo writer cuts the abnormal part off the magnetic tape to correct it. However, this process eventually ends up wasting the magnetic tape.
To eliminate this waste, this inventor conceived another servo writer. This servo writer, if an abnormality is detected, erases the abnormality, then rewrites a new servo signal on the erased part, and checks whether or not the servo signal is written successfully, by using a re-verifying head positioned downstream of the verifying head (see Japanese Unexamined Patent Application No. 2003-141836 (paragraphs 0012 to 0030, FIG. 1)).
This servo writer can eliminate the cutting process, thereby preventing the waste of the magnetic tape.
However, it can be expected that the transport speed of magnetic tapes will have been increased in the future. In order to follow this trend, a simplification of the procedure for correcting the abnormality is in demand.
The present invention has been conceived in order to meet the above demand. An object of the present invention is to provide a servo writer which adopts a simplified procedure for correcting abnormalities of servo signals written on tape-shaped recording media, thereby allowing for an increase in the transport speed of media in the future.